1. Timely restoration of sinus rhythm is strongly advisable in pregnant women with tachyarrhythmias and underlying heart disease.
2. Most therapies such as catheter ablation and antiarrhythmic drugs are relatively safe in pregnancy; amiodarone should be avoided in breastfeeding women because it is secreted at high levels in breast milk.
3. Direct current cardioversion is safe, although attention should be paid to airway management because of the risk of aspiration/regurgitation of gastric contents; care should also be taken to avoid the supine position because of its accompanying risk of aortocaval compression. Fetal monitoring is advisable because rare cases of fetal bradycardia have been reported after direct current cardioversion.
Published cardiac screening studies  show the incidence of arrhythmias in female students in junior high school and university and in women aged 35–40 years to be 1.9–3.6%. Extrasystoles, first- or second-degree atrioventricular block (AVB), and right bundle branch block are all common in women of childbearing age. Complex arrhythmias are extremely rare, however.
New onset, or an increased frequency of pre-existing arrhythmias, is observed during the course of pregnancy in otherwise healthy women because of maternal neural, hormonal, and physiological changes. Most of these arrhythmias are benign and asymptomatic, and without clinical significance.[2,3] Arrhythmias seen during pregnancy include premature supraventricular or ventricular extrasystoles, supraventricular tachycardia (SVT) such as paroxysmal supraventricular tachycardia (PSVT), atrial fibrillation (AF), atrial flutter (AFL), ventricular tachycardia (VT), and conduction disturbances including complete AV block, Wolff–Parkinson–White (WPW) syndrome, and QT prolongation. The exact incidence of each arrhythmia during pregnancy is unknown but arrhythmias other than monofocal or multifocal extrasystoles or couplets/triplets of supraventricular extrasystoles are rare. Ectopic beats are usually benign and present in a third of healthy pregnant women. Management consists mainly of reassurance.
The incidence of PSVT and VT in the normal population is reported to be <0.5%. In a study based on Holter monitoring analysis in volunteers during pregnancy, 95% of women showed supraventricular and/or ventricular extrasystoles but none showed complex arrhythmias. Ventricular extrasystoles are observed in up to 60% of pregnant women. Supraventricular tachyarrhythmias during pregnancy are not frequent. Nakagawa et al. studied 11 women with new-onset ventricular arrhythmia during pregnancy. In all, 73% of these originated from the right ventricular outflow tract; postpregnancy, the arrhythmia disappeared completely in all women.
The incidence of pre-excitation arrhythmias such as WPW syndrome varies from 0.1 to 3.7 per 1000 population. Most adults with a pre-excitation syndrome have a normal heart. The incidence of PSVT increases during pregnancy in women with WPW. However, pregnancy does not appear to predispose otherwise healthy hearts to AFL and AF. AFL and AF are usually observed during pregnancy in women with heart disease. VT is rare in the general population. Idiopathic VT with a right ventricular focus has been observed during pregnancy. In one study of 50 healthy pregnant women, who underwent Holter monitoring, only 1 episode of 3-beat VT was recorded.
In studies of long QT syndrome, especially in women with type 2 long QT syndrome, arrhythmic events such as syncope or cardiac arrest were observed more frequently postpartum than during pregnancy. Beta-blockers produce a significant reduction of arrhythmic events and are thus useful in the management of pregnant women with long QT syndrome.
The incidence of bradyarrhythmias is lower than that of tachyarrhythmias during pregnancy. Most are asymptomatic and have no clinical importance. The incidence of sinus node dysfunction during pregnancy is unknown, but clinically relevant cases are rare. Complete AVB has been observed during pregnancy; it is unclear, however, whether a woman with complete AVB would benefit from elective implantation of a permanent pacemaker. If there is no associated heart disease and a woman remains asymptomatic with a good ventricular escape mechanism, then a pacemaker is not necessary. In patients with permanent pacing in situ, the heart rate (HR) can be increased/adjusted to suit the stage of pregnancy.
Bundle branch block (BBB) appearing de novo in pregnancy has not been reported, but pregnant women may present with fascicular blocks, isolated or in combination with right BBB. Left BBB is very rare in women of childbearing age and, when seen, is usually associated with significant heart disease. Supraventricular and ventricular arrhythmias requiring treatment are rarely seen during pregnancy in healthy women.[12,13]
In an international multicenter study reported in 2013, the incidence of supraventricular arrhythmias was most frequent in valvar heart disease (3.0%), followed by cardiomyopathy (1.1%) and congenital heart disease (CHD) (0.7%). Ventricular arrhythmias were most frequently observed in cardiomyopathy (11%), followed by congenital heart disease (1.6%) and valvar heart disease (0.6%).
Recently, increasing numbers of women with repaired CHD have been reaching childbearing age, and CHD is the most frequent underlying structural abnormality observed during pregnancy. The prevalence of arrhythmias in repaired CHD and other structural heart disease increases with age as a result of surgical scars and the underlying lesion specific to each patient (some lesions produce intrinsic conduction abnormalities). In spite of improvements in the antiarrhythmic treatment available, some of these arrhythmias have a significant negative impact on life expectancy.
Arrhythmias in women with structural heart disease during pregnancy may be attributable not only to dramatic changes in hemodynamics, hormones, catecholamine levels, and autonomic nervous activity during pregnancy  but also to the presence in the heart of surgical scars and the underlying specific hemodynamics of any structural abnormality. Intravascular volume increases the preload on the heart during pregnancy and can reveal an arrhythmogenic focus in atrial or ventricular tissue, which is augmented by the underlying hemodynamic abnormalities. Poor functional status and a history of pre-existing decompensated cardiac failure are additional risk factors for arrhythmias.[14,15] During pregnancy, there is typically an increase in HR, which may promote arrhythmias by modifying the effective refractory period, the velocity of conduction, and the spatial dispersion of refractoriness. A rapid HR is induced by increased sympathetic or impaired parasympathetic nerve activity and can be accompanied by significant SVT or VT during pregnancy. Volume overload with neurohormonal activation and imbalance between sympathetic and parasympathetic systems secondary to inhibited autonomic nerve function may also play a contributory role.
The mechanism of VT in postventriculotomy women with CHD is typically reentry, involving a disparity in conduction between normal and diseased myocardium or operative scar, which is usually located adjacent to the ventriculotomy scar. In contrast, the most common mechanism of VT in pregnancy may be increased catecholamine sensitivity. This hypothesis is supported by the observation that increased rest during pregnancy decreases the incidence of SVT or VT. In one study, a blunted heart-rate response during exercise in pregnancy in women with CHD after repair (especially in tetralogy of Fallot [ToF]) was reported.
Arrhythmias (especially SVT, VT, and advanced AVB) during pregnancy in women with heart disease can cause significant hemodynamic compromise to both the mother and fetus. Prompt and accurate diagnosis and treatment of these arrhythmias is likely to reduce maternal and fetal morbidity and mortality. In one report, no maternal deaths were observed in women with repaired CHD and arrhythmias during pregnancy. However, it should be remembered that pharmacological agents used for arrhythmia control during pregnancy might have adverse effects on the mother and fetus.
Of the various reviews of pregnancy in women with CHD,[15,18–20] none have focused specially on arrhythmia during pregnancy. In a series reported in 2003, the incidence of significant arrhythmias during pregnancy in women with CHD was 6.9%, with SVT being more frequent than VT. The incidence of arrhythmias, including supraventricular and ventricular premature beats, during pregnancy in women with repaired CHD is high. However, the prevalence of clinically significant arrhythmia was reportedly less than 10%. In a report of 233 pregnancies among women with CHD, 20 of them developed arrhythmias (including two women with AFs and four with SVTs). In another study of 132 pregnancies, there was one case of VT and four of SVT, and in a multicenter study of 445 pregnancies, 2 women with VTs and 14 with SVTs were reported. Finally, only one woman was reported to have clinical arrhythmia in another study of 309 pregnancies.
SVTs may be associated with atrial dilatation, for example secondary to atrioventricular valve regurgitation, atrial septal defect, or Fontan procedure. Pregnancy may cause an increase incidence of paroxysmal AF in women with CHD. VT has been observed in women with repaired ToF, with free pulmonary regurgitation and right ventricular dilatation, and can induce right ventricular failure and sudden death. VT, especially if sustained, is reported to be unusual in pregnancy, and is relatively rare even in women with CHD. However, sustained VT requires urgent treatment when it does occur.
The precise incidence of new-onset sick sinus syndrome during pregnancy is unknown, but pregnancy does not appear to predispose women to develop second to third degree AVB. Complete AVB or sick sinus syndrome is sometimes seen as a surgical complication, but occurred rarely in a cohort with women with CHD requiring surgery. 
Data on the effect of antiarrhythmic medication on the fetus are very limited.[17,23] Most such drugs are either in the US Food and Drug Administration (FDA) Category C: “animal studies have shown an adverse effect on the fetus (teratogenic or embryocidal or other) and there are no adequate and well-controlled studies in pregnant women” or “no animal studies have been conducted and there are no adequate and well-controlled studies in pregnant women”: www.perinatology.com/exposure/Drugs/FDACategories.htm.
Especially during the first trimester, the administration of drugs is probably best avoided owing to the possibility of unknown adverse effects on the fetus. Most drugs have not been thoroughly tested in pregnancy and, as far as is currently known, all antiarrhythmic drugs can cross the placenta. Most are also transmitted from mother to baby through breastfeeding. The altered risk/benefit ratio of antiarrhythmic therapy during pregnancy in women with CHD affects the traditional concepts of management. Most SVTs and VTs of short duration (i.e. nonsustained) are benign and are not usually associated with any symptoms other than palpitations. Treatment of arrhythmias may be more harmful than the arrhythmia itself in this situation. However, some episodes of tachyarrhythmia can be associated with severe or even life-threatening symptoms in women with CHD. When considering therapy for cardiac arrhythmias, and sometimes for subsequent cardiac failure, the altered hemodynamics of pregnancy needs to be taken into account. Occasionally, immediate medical attention is indicated, especially for persistent SVT, sustained VT, or severe bradyarrhythmias. These can adversely affect the mother and fetus, resulting in hemodynamic compromise that jeopardizes not only the mother’s but also the fetus’s well-being (by decreasing uterine blood flow). In this situation, antiarrhythmic medication must be initiated as soon as possible after the diagnosis has been established.
VT can occur in a structurally normal heart, but it is more commonly associated with structural heart disease. In one study, nonsustained VT was observed in 3 out of 26 women with CHD. One woman with a repaired ToF developed VT during delivery and was successfully treated with intravenous mexiletine. In the series reported by Brodsky et al., 2 of the 40 women with VT during pregnancy died. The risk of death is further increased with concomitant ventricular dysfunction. Thus, in women with heart disease and symptomatic VT during pregnancy, antiarrhythmic therapy is clearly required. Lidocaine, mexiletine, or procainamide can be administered safely and effectively in cases of sustained VT with stable hemodynamics. Beta-blockers can also be effective for VT originating from the right ventricular outflow tract.
SVT is observed more frequently than VT, and two-thirds of patients with SVT will need treatment with antiarrhythmic medication. When SVT is observed in women with a low functional class (lower than New York Heart Association class II) or signs of heart failure, antiarrhythmic therapy should be initiated as soon as the diagnosis has been confirmed. In women with a history of paroxysmal SVT before pregnancy, the recurrence rate during pregnancy is high (36–50%), so catheter ablation should be considered before pregnancy. In cases of sustained VT or persistent paroxysmal SVT with unstable hemodynamics, prompt direct currect (DC) synchronized cardioversion should be offered without delay.[24,25]
PSVT includes a number of different types of tachycardia with varying features and clinical mechanisms, such as sinus nodal reentry tachycardia (SNRT), intra-atrial reentrant tachycardia (IART), atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reciprocating tachycardia (AVRT), automatic atrial tachycardia, multiple atrial tachycardia, AF, and AFL. Intravenous adenosine infusion is effective in most cases of PSVT. Beta-blockers are safe for the prevention of paroxysmal SVT long-term. A selective beta-1 blocker, for example metoprolol, is safer than a nonspecific beta-blocker, especially in the first trimester. In cases of drug-resistant incessant PSVT, catheter ablation can be performed. Pre-excitation may be associated with Ebstein anomaly and left ventricular noncompaction. AF with pre-excitation carries the potential risk of rapid conduction over the accessory pathways, permitting an extremely rapid ventricular response that can lead to ventricular fibrillation. Meticulous care should be taken in the use of digoxin and verapamil because both may increase transmission of impulses through the accessory pathway to the ventricle.
Short runs of AVNRT and AVRT require no treatment. However, prolonged episodes can occur in women with heart disease, producing hemodynamic compromise and requiring medication or even cardioversion. Adenosine has been shown to terminate more than 90% of SVTs involving the AV node as part of the reentry circuit, and it has been shown to be safe and useful during pregnancy. Intravenous verapamil may be used, but the safety of verapamil during pregnancy is not fully established.[22,26] For AVRT, the use of procainamide to slow the conduction of the bypass tract can also terminate the arrhythmia. For women with severe symptoms, a combination of digoxin and beta-blocker appears to be safe and effective during pregnancy. In women with AVNRT, digoxin or a beta-blocker can be useful. For severely symptomatic women who become refractory to drug therapy, radiofrequency ablation of the bypass tract or slow pathway has been successfully performed during pregnancy.
SNRT and IART can be managed by blocking either AV nodal conduction or the recurrent reentry circuit. Digoxin or a beta-blocker is safe and effective. Type Ia drugs can be used to terminate a reentrant circuit. Flecainide has been reported to be useful for the termination of atrial tachycardia during pregnancy.
Chronic AFL is usually associated with significant heart disease. It may occur as a result of increased atrial pressure, atrial dilatation, postsurgical scarring, or unusual hemodynamics such as more than moderate atrioventricular valve regurgitation, atrial switch operation of complete transposition of the great arteries (dTGA), or Fontan circulation. The approach to AFL in pregnant women depends on the degree of hemodynamic compromise. The mechanism of AFL often involves atrial macroreentry, or, rarely, focal ectopic origin due to enhanced automaticity. In common types of AFL, the atrial depolarization is usually seen as a negative deflection in the inferior leads (II, III, and aVF) of the electrocardiogram. In a hemodynamically stable woman, the ventricular rate can be controlled with intravenous digoxin. Beta-blockers and/or digoxin are also safe and are usually effective for rate control. In resistant cases, calcium channel blockers can be used. Alternatively, class I antiarrhythmic agents such as procainamide can be used to convert AFL to sinus rhythm. In women with severe heart disease and hemodynamic compromise, urgent synchronized cardioversion should be employed.[25,28] The need for continuing medication for sinus rhythm maintenance will depend on the severity and frequency of the symptoms.
In women with heart disease, pregnancy can cause an increased incidence of AF. The increased morbidity and mortality in such cases can be explained by hemodynamic changes and the increased risk of thromboembolism, especially in the third trimester with its hypercoagulable state. Hemodynamically, AF is poorly tolerated in women with inflow stenosis (mitral valve stenosis, tricuspid valve stenosis, increased ventricular end-diastolic pressures). Atrial emptying is severely impaired because of the shortened diastolic filling time. This results in a rise in atrial and pulmonary venous pressure, followed by pulmonary edema and decreased cardiac output. The risk of systemic embolization in AF during pregnancy is probably due to circulatory stasis in the atrium and left atrial appendage, and the hyperviscosity and hypercoagulable state of pregnancy, with subsequent thrombus formation.
The etiology of AF can be associated with postoperative scarring and increased atrial pressure. The most common cardiac conditions associated with this arrhythmia during pregnancy are mitral or tricuspid stenosis, at least moderate CHD (i.e. after repair of ToF), dTGA (atrial switch repair), systemic ventricular inflow and outflow stenosis of the ventricles, atrioventricular valve regurgitation and more complex CHD such as the Fontan procedure. Electrophysiologically, AF is due to the simultaneous discharge of multiple atrial foci, resulting in a high atrial rate and no apparent P waves in the ECG. The ventricular rate depends on atrioventricular nodal refractoriness.
The management of AF is similar to that of AFL. In a hemodynamically stable woman, the ventricular rate can be controlled by digoxin, a beta-blocker, a calcium channel blocker, or a combination of these. As an alternative to rate control, drugs such as procainamide may be useful for conversion to sinus rhythm.[28,29] Synchronized cardioversion should be applied to convert AF to sinus rhythm in women with compromised hemodynamics. In an elective situation, procainamide should be started and a therapeutic level achieved before cardioversion to prevent relapse. In emergency cases, cardioversion is the treatment of choice provided there is no atrial thrombus, as assessed by transesophageal echocardiography.
An electric shock, by depolarizing all excitable myocardium and possibly by prolonging refractoriness, interrupts reentry circuits, discharges foci, and establishes the electrical homogeneity that terminates reentry. DC cardioversion will terminate most tachycardias effectively, whether SVT or VT, at any stage of pregnancy. Electrical cardioversion is the treatment of choice for all drug-refractory maternal arrhythmias, and can be performed safely during pregnancy. Reported fetal complications from DC cardioversion are very few, including fetal bradycardia, which normally resolves spontaneously. Nevertheless, it is good practice to scan the fetal heart immediately after successful DC cardioversion of the mother.